1. Field of the Invention
The present invention relates to the field of display technology, and in particular to a thin-film-transistor (TFT) substrate structure and a manufacturing method thereof.
2. The Related Arts
Amorphous silicon (a-Si) is the most widely used semiconductor material in the semiconductor industry. The a-Si material shows a great potential difference when put in contact with metals, making it hard to form an ohmic contact. In practical applications, in order to make an ohmic contact between a metal and a semiconductor, it is commonplace to heavily dope element P in a surface of the semiconductor for lowering the contact resistance between the metal and the semiconductor and increasing current efficiency.
FIG. 1 is a schematic view, in a sectioned form, showing a conventional thin-film transistor (TFT) substrate structure. The TFT substrate structure comprises a base plate 100, a gate terminal 200 formed on the base plate 100, a gate insulation layer 300 formed on the base plate 100 and covering the gate terminal 200, an amorphous silicon layer 400 formed on the gate insulation layer 300 to correspond to the gate terminal 200, and a source terminal 500 and a drain terminal 600 formed on amorphous silicon layer 400 and the gate insulation layer 300. The amorphous silicon layer 400 has a middle portion that is downward recessed so as to define a channel zone 450 located above and corresponding to the gate terminal 200. The amorphous silicon layer 400 has a surface that is doped with ions at portions thereof respectively corresponding to two sides of the channel zone 450 so as to form first and second N-type heavily-doped zones 410, 420. The source terminal 500 and the drain terminal 600 are respectively set in contact with the surfaces of the first and second N-type heavily-doped zones 410, 420.
FIG. 2 shows a curve of a leakage current of an a-Si device involving the TFT substrate structure of FIG. 1. It is known from FIG. 2 that certain problems exist when an operation current (Ion) of the TFT substrate structure is increased. When the loading voltage reaches a predetermined level, positive charges are induced so as to generate a hole-conducting channel. The leakage current (Ioff) is thus increased, making the curve severely bent and leading to a reliability issue.
Thus, it is desired to provide a TFT substrate structure and a manufacturing method thereof that overcome the above problems.